Recently, technologies for providing various wireless communication services through a terminal have been developed. Wireless communication services include, for example, a Code Division Multiple Access (CDMA) service, a Global System for Mobile communication (GSM) service, and a Wireless broadband (Wibro) service.
In order to provide various wireless communication services, a frequency synthesizer that has a broadband voltage controlled oscillator (VCO) capable of accommodating frequency bands required by the wireless communication services is desired. When a wireless communication service is changed, a frequency synthesizer changes a frequency within a frequency band which is manually selected from among multiple bands of a VCO for dividing a broad bandwidth into multiple bands, or changes a frequency through a VCO frequency band which covers multiple frequency bands.
However, there are difficulties in applying a technique of changing a frequency within a band that is manually selected to wireless communication services requiring fast channel switching.
Meanwhile, a technique of changing a frequency using a VCO that covers multiple frequency bands may reduce a time required for channel switching, but may deteriorate noise characteristics of a frequency synthesizer because the VCO gain is relatively high.